- The study group consisted of polycystic ovarian syndrome(PCOS) patients diagnosed according to the Rotterdam criteria. The investigators defined Clomiphene citrate (Clomid, Iran hormone,Tehran,Iran) resistance as anovulation after consumption of 3 cycles of cc at 150 mg/day, determined by serial estradiol monitoring and sonography. Patients resistant to Clomiphene citrate became candidates for letrozole (Femara,Novartis,Quebec,Canada) consumption at the step-up of the protocol. Patients were between 18 and 39 years of age, body mass index (BMI) was > 19 or < 30 kg/m2 and day 3 follicle-stimulating hormone (FSH) < 12Miu/Ml.